About this Show

Sino News Magazine

News/Business.

NETWORK
PBS

DURATION
00:30:00

RATING

SCANNED IN
San Francisco, CA, USA

SOURCE
Comcast Cable

TUNER
Channel 107 (693 MHz)

VIDEO CODEC
mpeg2video

AUDIO CODEC
ac3

PIXEL WIDTH
528

PIXEL HEIGHT
480

TOPIC FREQUENCY

Us 7, Indiana 5, Gilbertson 3, Pennsylvania 3, Oregon 3, Grimm 3, Stephen Long 2, La La 2, Parke 2, William Howe 2, Massachusetts 2, Washington 2, America 2, La 2, Vermont 2, Theodore Burr 2, New England 2, United States 1, Adz 1, Brown 1,
Borrow a DVD
of this show
  PBS    Sino News Magazine    News/Business.  

    January 2, 2011
    8:30 - 8:59pm PST  

8:30pm
"spanning time: america's covered bridges" has been provided by -- additional support has come from viewers like you. you can go to gardens, you can go to plays. but they're nothing like covered bridges. announcer: folks, if you would like to go with us on our last guided bus tour of the day, leave the driving to us, sit back, relax, hear the history of our county, the history of our bridges and the builders. good afternoon, everyone, and welcome to parke county, the covered-bridge capital of the world. we originally had 52 1/2 covered bridges. at present day, we have 31.
8:31pm
i'm aboard a school bus with a lot of other folks, about to look at old bridges in a rural county in indiana. it's all part of the parke county covered bridge festival. ten days in the fall, when the local residents celebrate and make a little money from the fruits of their ancestors' labor. now, one might question the utility value of covered wooden bridges in the 21st century. yet there is no doubt they still capture our imagination. tourists flock to them. small fortunes are spent to restore them. and for many of us, they evoke fond, and maybe even romantic, memories. ♪ there's an old covered bridge ♪ ♪ 'cross the old mill stream ♪ covered with memories for me ♪ ♪ it was there ♪ in my childhood ♪ i used to dream
8:32pm
♪ that my bridge was a ship ♪ ♪ far at sea grimm: visiting a covered bridge is taking a few steps back in time. most were built a hundred or more years ago, at a time when horses carried the load, travel was tough, and life in general was a lot slower. ♪ just the old covered bridge ♪ ♪ 'cross the old mill stream ♪ covered with memories for me ♪ [ horn honks ] man: the simplest way i could explain what a covered bridge represents is just a piece of our history and a chance to look back at the past a little bit. covered bridges are one of the few things that our great-great-grandparents built or paid for that we can still use. covered bridges tell us a lot about the past,
8:33pm
in sort of the obvious graphic way about how things might have looked. they tell us that cars were smaller, there weren't big trucks, they tell us this is the scale of transportation facility that were needed in the 19th century and early 20th century. one can look at a bridge like this, for example -- there's a lot of ways to look at it -- but one way it could be looked at is a document. because very little has changed here. there's an immense amount that can be found out from a covered bridge, depending upon your imagination and how far you want to go with it. [ shutter clicks ] okay. man: there's a lot of people who like bridges, and especially the wooden ones. they travel throughout the country looking at them. and some of them actually, they're funny, they count them like it's a competition. they'll come, jump out, photograph, jump in, go. get to the next bridge. [ laughing ] others will spend hours here, you know. woman: i have not met many people who have not had some experience
8:34pm
or story to tell about a covered bridge. and the bridgeton covered bridge is an area that's dear to my heart. seven generations of my family have walked across the boards of this covered bridge. my personal reasons for liking covered bridges, loving covered bridges and getting so involved with it, is that they're a wonderful, historic practical solution to crossing rivers. this is an adz, the favorite tool of the 19th-century carpenter. bridge-builders used it, along with a broad axe to square off logs into timbers. these are some of the other tools the builders used. hand saws -- this one took two people -- draw knives... augers... and my favorite, the hand boring machine. it's basically an early drill press.
8:35pm
put it on the timber, sat here, turned these handles. before you know it, you had a hole. power tools weren't invented yet, and heavy materials were lifted with a rudimentary crane called a gin pole. the choice of building material itself was easy. the earliest bridges were built with what was around -- wood. lots and lots of wood. gilbertson: construction was much more local. they didn't bring in concrete, they didn't bring in steel. they brought in wood from just a few miles away from the bridge, to build it with. in new england, we use mostly, spruce is the more popular wood. some are hemlock. and there are a few that are made of white pine. typically, most of the bridges in oregon are built out of fir. these are built out of fir that originally
8:36pm
came from the timber around the area. spruce was used around here because it was available in big pieces, and it's light for how strong it is. if you don't have spruce, you haven't got as good choices, and you have to go to hard wood. although many early bridges were made of white pine, which we generally don't use now, because it's thought not to be strong enough. but the virgin old-growth white pines, slow-grown, really straight-grained, had such virtues, you might say, and quality that it made up for whatever strength properties the modern engineer thinks it lacks. gilbertson: the traditional craftsmen knew a lot about wood. modern engineering analysis uses averages. the timber framers picked their wood carefully for strategic spots in the bridge. they knew where it had to be stronger. grimm: sometimes if you look closely, you can still see the marks left by the tools on the hand-hewn timbers. i'm inside the beanblossom covered bridge in brown county, indiana. this large beam at the top of the bridge
8:37pm
is called a cord. an adz, wielded by some anonymous indiana craftsman, left these marks almost 125 years ago. these things are made by hand. the wood was sawn, usually, but the rest of the joinery and the assembling of this stuff was all done by hand. and think of the courage it took and the energy it took. really, just, i mean, we have wonderful means, compared to what our ancestors had. and yet they build great things. the first bridges simply were trees that had fallen or logs placed across a stream. but a single log has its limitations. you have to be pretty agile to get even yourself across, especially in weather like this. so people added a second log
8:38pm
and then put boards across it, to make it wider. a primitive bridge like this can't be very long, or it sags and eventually collapses. that's where the truss comes in. now, the triangle is the only geometric form that will not collapse upon itself. so if you add a triangular structure called a truss to the sides of a bridge, it prevents the road bed from sagging. the simple triangle, reinforced in the middle with a post, becomes the most basic bridge truss design. it's called a king-post truss. this part is the actual king post. if you open the triangle up a little and add another post, it becomes a queen-post truss. man: the ebenezer bridge is a great example of a queen-post truss. and actually, you might even be able to see, by looking through the siding of the bridge, you can see the beams inside.
8:39pm
you can see what is shaded a little differently on the exterior of the bridge. that's a queen-post truss design, very, very typical for a shorter span. some of the smaller types, the queen-post, king-post, are good for the short little small crossing, small streams. lewandoski: the single king post, you're probably not good with vehicles going over it for much more than 30, 40 feet. you can take queen post up to maybe 70 or 80 feet. as the length of a bridge increases, the simple triangular truss becomes impractical, because it would need to be too high. so, as 19th-century builders attempted longer and longer spans, they developed a variety of much more complicated truss systems. the more successful ones still exist. connecticut architect ithiel town devised and patented his ingenious town lattice truss. this truss continues to hold up many of the covered bridges in new england. graton: in some ways, it's a simple truss, but in other ways,
8:40pm
it's quite complicated. [ laughs ] it's just a lattice of timber, which, if they are assembled correctly, they are a very, very durable truss. lewandoski: a lattice truss has got a lot going for it -- it's redundant. you could probably run around one of these bridges, cutting through lattices with a chainsaw, and the bridge won't fall down, because there's multiple load paths, you might say. they were easy to build. i mean, they require careful work, but you're really just laying plank upon plank and drilling through it, over and over again. and you can make them to all sorts of lengths. they're flexy, but they're hard to kill. that's the main thing about them. they're a very appealing sort of truss.
8:41pm
grimm: as far back as ancient rome, people knew that the arch was a great way to span a long distance. when you're building a timber bridge, the arch distributes the weight and carries it to the abutments on the end. and it does this without adding a lot of extra wood. one particular 19th-century arch design dominates american covered bridges. probably the most popular is the burr truss, which was invented by theodore burr and was patented in 1804. theodore burr was originally from connecticut, but he did his primary bridge-building here in pennsylvania. graton: the burr arch is a great truss. the only drawback, i think, is that it's more time-consuming to frame it in and frame it correctly. there's a lot of joinery in a burr arch that, once it's put together, you really can't see, if it was done correctly, and it's a good tight-fitting joint or not,
8:42pm
and of course, that bridge depends on a good, tight-fitting joint. the paddlefoot is another one that, once it's put together, you can't see the joint. can't see what's going on in there, so you've got to trust that the framer fitted it and got it together so it's working, not just looking pretty. in 1840, william howe, a massachusetts house-builder and mill-wright, revolutionized timber truss construction. he introduced these iron tie rods to prevent the uprights from pulling apart. long after the bridge was in service, a nut at the top could be turned to adjust the rod's tension,
8:43pm
ensuring that the timbers stayed together. the howe truss became a favored truss design for bridges that needed to carry heavy loads. railroad companies throughout the country adopted the design, and when its patent expired in the 1860s, the howe truss quickly moved west. leedham: in oregon, we've got 51 howe's bridges. 40 of those bridges are howe trusses, similar to what we have here. but a howe truss is a simple
8:44pm
truss to build. holds quite a bit of weight, and it can be very easily braced so that the weight doesn't affect the stability of the bridge itself. actually, the howe truss was just an improvement on an earlier truss called the long truss. stephen long realized the importance of stiffness in a bridge, the need for everything to be tight and stay tight as traffic went across. and he worked out the basic geometry we find in the howe truss, but because wrought iron was not very common in 1830, stephen long built his truss using wood for the verticals. william howe advocated replacing the timber verticals with wrought-iron rods that could be more quickly installed and more easily adjusted later. there's only so many trusses that people invented that really work. the bridges that are surviving now are generally pretty good ones.
8:45pm
most people realize that the trusses hold a bridge up, but the purpose of the bridge's covering is less obvious. just exactly why are these bridges covered?
8:46pm
wow, you know, that is a good question. i understand that back in the olden days, that's where they took cover when it rained, with the buggies. um, maybe so they wouldn't be slippery for when it snows? oh... i haven't the slightest idea. [ laughs ] the cover covers over the people so they don't get all wet from the rain, say, or the snow. probably to keep the rain off you -- i have no idea. i know in alaska, they have one, and it's to keep the ice from building up. protection. no, is this a trick question? it's where they get the strength in the structure to support weight. it's not from underneath, it's from the top of the structure, is where the strength is. mostly have them covered so that the horses don't see with the water and get scared and bolt. well, you know, i asked that same question. and nobody really knew.
8:47pm
a good place to make out? [ laughing ] [ laughs ] it's like the tunnel of love. not that i've done it. actually, people used to park on them and fish. they'd get wet, so that's why they covered them. oh, i know the answer to this one, and i can't remember it! i don't know. i don't remember, i'm sorry. let me ask you! you're a native, i can tell. you know, i'm 3,000 miles away. why are they covered? to keep the truss from rotting. no other reason. and it's very clear from contemporary stuff from the early 19th century, when they were discussing what the economics of covering wooden bridges -- because lots were built uncovered -- that if you want to keep wood from rotting, you have to keep lots of moisture out of the joints. wood can take some moisture, as long as it can dry out, but it can't have water laying in places and staying there a long time. that's the reason for doing it. it's not because horses get scared. it's not because of any other reason --
8:48pm
because there were probably a larger number of uncovered wooden bridges at the same time there were covered bridges. they were practical people. if you build an open bridge, i don't care how good the truss is, and leave it exposed to the weather, it might last seven, eight, nine, ten, twelve years, something like that. minute you cover it -- well, the longevity of it has increased probably six, seven, eight, or tenfold. so why rebuild the bridge when you can cover it and not have to fool with it for a while? grimm: although covered bridges have been around in europe for several centuries, america's very first covered bridge wasn't completed until 1804. it crossed the schuylkill river on market street in philadelphia, pennsylvania. barker: george washington and ben franklin never saw a covered bridge. most covered bridges were built in the 1870s and the 1880s. but the american engineers didn't know much about the european experience, and developed independently. [ fiddle music playing ]
8:49pm
grimm: by the 1890s, over 12,000 covered bridges spanned american rivers and streams. today, only about 800 remain. we lost this one in a flood.
8:50pm
wright: wind storms, hurricanes, high water, they've been the traditional enemies. our ancestors didn't have the hydrological data that we have. they didn't know what the 100-year flood was. so it was a little bit of a guess how high the water was going to come. they'd base -- "oh, well, gee, "for the past 30 years, it hasn't been "any higher than that, so if we set the bridge 10 feet above that, we're safe." then along comes a big flood, and the bridge is gone. i think in the '27 flood in vermont, 1927, i think 400 were lost in that flood alone, leaving about 200, and it's trickled its way down to about 100 now. grimm: sometimes nature caused the losses. other times, people simply believed that the covered bridges hindered progress. you bump into people like that from time to time.
8:51pm
"oh, get rid of the damn thing, i can't get my logging truck through here." you know, or "i can't bring my ten-wheeler through with a load of gravel." there was a bridge down in massachusetts, it was one of the new covered bridges -- it was built in the 1950s. new sheffield covered bridge. and there were interests in the town who were involved in trucking. in fact, one of them sat on the board of selectmen, and so the bridge disappeared. there's now a steel-and-concrete bridge there. oregon lost so many of its covered bridges due to the pressure put on the counties by the timber and logging industry to provide bridges that could carry the heavy truck traffic that carried the logs to the mills. at the beginning of that program, typically, the covered bridge was just removed and replaced with a new concrete bridge. after some negative reaction by the local residents around the covered bridges,
8:52pm
they started building new concrete bridges immediately adjacent to the historic covered bridge, which essentially destroyed the setting and the aesthetic of the covered bridge. now, you know, everyone wants to be able to drive their vehicle, whatever the size it is, you know, whatever load it is, and sometimes it's real hard to convince those guys that they should go a couple of miles around, rather than try to get through that bridge. gilbertson: there is a bridge about 15 years ago that an ill-advised truck driver -- posted for 10,000 pounds -- went over it with a stamped 60,000-pound load ticket, and the bridge literally exploded. it's the only catastrophic collapse of a covered bridge that i know of. careful driving and good maintenance can extend the life of a covered bridge indefinitely. however, nature and adventurous teenagers often make maintenance a challenge.
8:53pm
♪ la, la la, la la, la ♪ hey bea! hey margie! ♪ ♪ say, jerry! come on and go with us! ♪ ♪ let's go to the kissing bridge! ♪ ♪ oh! great idea rudy! ♪ ♪ wow! let's go! ♪ ♪ to the old kissing bridge on a cold christmas day ♪ ♪ every boy took his girl for a ride ♪ ♪ on a sleigh and they stopped ♪ ♪ and they kissed ♪ so they always had a very merry christmas ♪ ♪ to the old kissing bridge ♪ with its roof made of wood ♪ every old-fashioned wolf ♪ took his red riding hood and they stopped ♪ ♪ and they kissed ♪ and they really had ♪ a very merry christmas leedham: this is an example of some of the maintenance headaches that the counties have, the graffiti that the kids have put onto the bridge -- though some of it can be quite historical.
8:54pm
the other problems that they have is the kids punching holes in the roof to swim in the stream below. these holes are holes that were made for fumigation, for bugs and rot. wood rots from the inside out. you wouldn't know it to look at it, so they drill with a hollow tube and determine how much rot is in there, if there is any rot. if they do determine that there are bugs or rot, then they can fumigate these to stop the bug infestation.
8:55pm
hoyne: timber, as we all know, just doesn't hold up well to a lack of maintenance, and then this harsh environment. and if you have a couple pieces of wood that you sandwich together, and moisture gets trapped in there, that's where we tend to find the rot. so rot of the timber is the single largest issue that we're faced with. many of them are on the dirt roads. the vehicles track in the sand, in the wintertime, that sand and wood gets wet, and if you don't clean that sand, it, again, traps the moisture. so, whether it's cleaning the sand, fixing the roof, fixing the siding, all these activities lead towards preventing moisture from getting at the bridge. if the bridge is covered and it's halfway decently taken care of, it'll outlast concrete bridges two or three times. the lifespan of a wooden bridge is actually indefinite.
8:56pm
grimm: unfortunately, maintenance issues pale before more serious threats. woman: most definitely the biggest problem we have is vandalism. man: yes, we have problems with people. anything that a man can do, they've probably tried or will try, on a covered bridge. people tried to burn our bridges down. we've had people try to blow them up. probably the biggest danger is fire. you know, arson. i think that probably takes more covered bridges today than anything else. grimm: few covered bridges are immune to the arsonist's torch or the careless match. since 1992, over 35 covered bridges in the united states have been set ablaze by arsonists, or under suspicious circumstances. only 10 of those bridges have survived. in 2002, an arsonist burned iowa's cedar covered bridge, made famous by the movie
8:57pm
"bridges of madison county," and a year later, a second iowa bridge was destroyed. also in 2002, arsonists torched indiana's jeffries ford covered bridge. in some instances, the destruction may not be intentional, but the results are just as devastating. the saddest piece of my covered bridge experience was in swanton, vermont, where there was a covered railroad bridge that was 385 feet long. that bridge could carry a loaded train. the bridge burned through some carelessness of some kids that were drinking there, set it on fire. i went up the day after, and when the remains were still smoking, a father and a son came up and... the father told me his son had been begging him sunday to take him to the bridge and look at the bridge, and he said, "oh, we can always do that." and now he can't do it.
8:58pm
steps are being taken in many places to try to thwart the arsonists. there are some excellent flame retardants. there are also all kinds of fire detection systems that can be installed in covered bridges, some of them wired directly to the fire department. all the bridges the state of new hampshire owns, for example, are protected with a fire-sensing device, so that if anything happens, the fire department learns about it right off, quick. we try to instill a caring with our children in the county about the covered bridges, and we ask the neighbors and friends of the covered bridges to be vigilant. i like to think of it as, mother nature made the trees that the bridges were built from, and essentially mother nature also has created the bugs that are trying to eat the bridges, allows the rot and decay, and have also created the people
8:59pm
that constantly vandalize the bridges. [ dogs barking ] a burned bridge seriously damages a county's transportation grid. but in a place like parke county, indiana, site of the burned jeffries ford bridge, an assault on a covered bridge becomes an assault on a local economy. lynk: we have a small community here. there are only 17,000 people in all of parke county. and when we have the covered bridge festival, we have about two million visitors. tremendous influx of people that come here. we've had studies done, and an estimate is about a $30 million economic impact during the 10 days of the festival. every merchant thinks that christmas is the big time. in parke county, it's the covered bridge festival. tourism, in general, is a huge business for washington county in pennsylvania.